1. Field of the Invention
The present invention relates to a wireless charging coil structure in electronic products, particularly to a structure in which an insulated wire is wound on a magnetic conductor into a first coil, and the first coil is extended to a given length and then wound reversely into a second coil, so as to generate induced currents in the induction range between the first and second coils, making such structure applicable to transmission of power energy in devices with narrow inductive sections.
2. Description of the Related Art
Today, rapid developments in electronics and multimedia information result in the trend of lightness, thinness, shortness and miniaturization as well as multipurpose applications for handheld electronic devices, such as notebook and tablet computers, smart phones and personal digital assistants (PDA), making these devices be miniature in dimensions, lightweight and portable among other features. Besides, as software and hardware functions are developed one after another, the electronic devices can provide more practical applications and have been widely used as an essential part of our work, life and recreational activities.
Yet what is required in making handheld electronic devices portable, first of all, is the solution to power supply. The most common solution is to install rechargeable batteries in handheld electronic devices and provide a compatible power supply to recharge these batteries when electricity runs out. As handheld electronic devices are not manufactured according to the same specifications, however, different power supplies are needed to recharge these devices, and this may lead to significant increase in purchase costs. If there are many power supplies at hand, it will not only cause inconvenience in putting wires in order, but also require considerable space, in addition to inconveniences in placing or carrying them.
Thus, taking this problem into consideration, some firms have developed induction type power supplies, or known as wireless chargers, which are based on electromagnetic induction to transmit electric power and provide excellent convenience by supplying electric power by contactless electromagnetic induction. So these devices draw considerable attention upon launch in the marketplace. To put it simply, the method of supplying electric power by electromagnetic induction is to use two inductance coils for mutual induction of alternating current to transmit electric power on the principle similar to traditional wire-wound power transformers, followed by installation of induction coils in different electronic devices to support charging of these devices simultaneously, thus solving the problems of incompatibility of power supplies and inconvenience in carrying them effectively.
Induction type power supplies currently available in the market mostly rely on two coil modules as the power sourcing (PS) end to transmit electric power and power receiving (PR) end to receive electric power, and induction coils are required to be wound on magnetic materials of the coil modules, so that electric power can be transmitted through induction surfaces of the coil modules. Besides, the coil modules are designed to have considerable inductance and work with capacitors to generate resonance oscillations for wireless power transfer.
FIG. 7 shows a schematic drawing of an induction type power supply in conventional use. According to this figure, the induction type power supply originates and evolves from a power transformer at the early stage, in which separate toroid coils B are wound on central limbs of two E-shaped iron cores A, and air clearance of the iron cores is utilized for energy storage with low flux or leakage inductance. When applied in circuits of induction type power supplies, such design will cause too much loss of magnetic field induction in the process of coupling and thus reduce conversion efficiency. Though we may use larger E-shaped iron cores A to increase the effective sectional area, or increase the number of turns and enlarge air clearance to strengthen the ability of inducing electricity, it will result in overweight of E-shaped iron cores, making it inapplicable to handheld electronic devices that highlights portability.
Refer to FIG. 8, which shows a schematic drawing of another induction type power supply in conventional use. Such design prevails in wireless charging devices currently available in the market. According to this figure, the base plate C is wound by a hollow planar volute coil D used to transfer electric power inductively. Since wireless power energy is transmitted from both surfaces of the volute coil D at the PS end towards the volute coil D at the PR end, and cannot be fully received by the volute coil D at the PR end, the transmitted power energy may heat up surrounding devices or equipments and cause danger if absorbed by these devices or equipments. Therefore, for product design, the base plate C on which the volute coil D is wound must be made of magnetic materials capable of shielding electromagnetic waves.
Magnetic materials can reflect, absorb and transmit electromagnetic waves among other properties. To design a power supply with better power transmission efficiency, a common solution is to add magnetic materials with better reflection characteristics onto the uninduced surface of the volute coil D at the PS end as the base plate C and to add magnetic materials with better absorption characteristics onto the uninduced surface of the volute coil D at the PR end as the base plate C. Though such approach can derive better conversion efficiency, production costs cannot be reduced effectively due to difficulty in producing magnetic materials with reflection and absorption characteristics and considerably high prices of these materials. In addition, even though larger induction surface of the volute coil D wound onto the base plate C results in better capabilities to transfer and receive electric power by electromagnetic induction, since the volute coil D is shaped like a round, it is difficult to install the volute coil D in exquisite handheld electronic devices, thus making restrictions over integrated functions and effect of such power supply. As there is need to make further improvements in such regard, this is what those engaged in this field want urgently to research and improve.